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Message-Id: <1215874310-10534-2-git-send-email-gerrit@erg.abdn.ac.uk>
Date: Sat, 12 Jul 2008 15:51:47 +0100
From: Gerrit Renker <gerrit@....abdn.ac.uk>
To: davem@...emloft.net
Cc: dccp@...r.kernel.org, netdev@...r.kernel.org,
Gerrit Renker <gerrit@....abdn.ac.uk>
Subject: [PATCH 1/4] dccp ccid-3: Fix error in loss detection
The TFRC loss detection code used the wrong loss condition (RFC 4340, 7.7.1):
* the difference between sequence numbers s1 and s2 instead of
* the number of packets missing between s1 and s2 (one less than the distance).
Since this condition appears in many places of the code, it has been put into a
separate function, dccp_loss_free().
Further changes:
----------------
* tidied up incorrect typing (it was using `int' for u64/s64 types);
* optimised conditional statements for common case of non-reordered packets;
* rewrote comments/documentation to match the changes.
Signed-off-by: Gerrit Renker <gerrit@....abdn.ac.uk>
---
net/dccp/ccids/lib/packet_history.c | 73 +++++++++++++---------------------
net/dccp/dccp.h | 15 +++++++
2 files changed, 43 insertions(+), 45 deletions(-)
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -153,6 +153,21 @@ static inline u64 max48(const u64 seq1, const u64 seq2)
return after48(seq1, seq2) ? seq1 : seq2;
}
+/**
+ * dccp_loss_free - Evaluates condition for data loss from RFC 4340, 7.7.1
+ * @s1: start sequence number
+ * @s2: end sequence number
+ * @ndp: NDP count on packet with sequence number @s2
+ * Returns true if the sequence range s1...s2 has no data loss.
+ */
+static inline bool dccp_loss_free(const u64 s1, const u64 s2, const u64 ndp)
+{
+ s64 delta = dccp_delta_seqno(s1, s2);
+
+ BUG_TRAP(delta >= 0);
+ return (u64)delta <= ndp + 1;
+}
+
enum {
DCCP_MIB_NUM = 0,
DCCP_MIB_ACTIVEOPENS, /* ActiveOpens */
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -215,22 +215,19 @@ static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2
u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
s2 = DCCP_SKB_CB(skb)->dccpd_seq;
- int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
- d12 = dccp_delta_seqno(s1, s2), d2;
- if (d12 > 0) { /* S1 < S2 */
+ if (likely(dccp_delta_seqno(s1, s2) > 0)) { /* S1 < S2 */
h->loss_count = 2;
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n2);
return;
}
/* S0 < S2 < S1 */
- d2 = dccp_delta_seqno(s0, s2);
- if (d2 == 1 || n2 >= d2) { /* S2 is direct successor of S0 */
- int d21 = -d12;
+ if (dccp_loss_free(s0, s2, n2)) {
+ u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;
- if (d21 == 1 || n1 >= d21) {
+ if (dccp_loss_free(s2, s1, n1)) {
/* hole is filled: S0, S2, and S1 are consecutive */
h->loss_count = 0;
h->loss_start = tfrc_rx_hist_index(h, 1);
@@ -238,9 +235,9 @@ static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2
/* gap between S2 and S1: just update loss_prev */
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);
- } else { /* hole between S0 and S2 */
+ } else { /* gap between S0 and S2 */
/*
- * Reorder history to insert S2 between S0 and s1
+ * Reorder history to insert S2 between S0 and S1
*/
tfrc_rx_hist_swap(h, 0, 3);
h->loss_start = tfrc_rx_hist_index(h, 3);
@@ -256,22 +253,18 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
s3 = DCCP_SKB_CB(skb)->dccpd_seq;
- int n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp,
- d23 = dccp_delta_seqno(s2, s3), d13, d3, d31;
- if (d23 > 0) { /* S2 < S3 */
+ if (likely(dccp_delta_seqno(s2, s3) > 0)) { /* S2 < S3 */
h->loss_count = 3;
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 3), skb, n3);
return 1;
}
/* S3 < S2 */
- d13 = dccp_delta_seqno(s1, s3);
- if (d13 > 0) {
+ if (dccp_delta_seqno(s1, s3) > 0) { /* S1 < S3 < S2 */
/*
- * The sequence number order is S1, S3, S2
- * Reorder history to insert entry between S1 and S2
+ * Reorder history to insert S3 between S1 and S2
*/
tfrc_rx_hist_swap(h, 2, 3);
tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n3);
@@ -280,17 +273,15 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
}
/* S0 < S3 < S1 */
- d31 = -d13;
- d3 = dccp_delta_seqno(s0, s3);
- if (d3 == 1 || n3 >= d3) { /* S3 is a successor of S0 */
+ if (dccp_loss_free(s0, s3, n3)) {
+ u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;
- if (d31 == 1 || n1 >= d31) {
+ if (dccp_loss_free(s3, s1, n1)) {
/* hole between S0 and S1 filled by S3 */
- int d2 = dccp_delta_seqno(s1, s2),
- n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;
+ u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;
- if (d2 == 1 || n2 >= d2) {
+ if (dccp_loss_free(s1, s2, n2)) {
/* entire hole filled by S0, S3, S1, S2 */
h->loss_start = tfrc_rx_hist_index(h, 2);
h->loss_count = 0;
@@ -307,8 +298,8 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
}
/*
- * The remaining case: S3 is not a successor of S0.
- * Sequence order is S0, S3, S1, S2; reorder to insert between S0 and S1
+ * The remaining case: S0 < S3 < S1 < S2; gap between S0 and S3
+ * Reorder history to insert S3 between S0 and S1.
*/
tfrc_rx_hist_swap(h, 0, 3);
h->loss_start = tfrc_rx_hist_index(h, 3);
@@ -318,33 +309,25 @@ static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
return 1;
}
-/* return the signed modulo-2^48 sequence number distance from entry e1 to e2 */
-static s64 tfrc_rx_hist_delta_seqno(struct tfrc_rx_hist *h, u8 e1, u8 e2)
-{
- DCCP_BUG_ON(e1 > h->loss_count || e2 > h->loss_count);
-
- return dccp_delta_seqno(tfrc_rx_hist_entry(h, e1)->tfrchrx_seqno,
- tfrc_rx_hist_entry(h, e2)->tfrchrx_seqno);
-}
-
/* recycle RX history records to continue loss detection if necessary */
static void __three_after_loss(struct tfrc_rx_hist *h)
{
/*
- * The distance between S0 and S1 is always greater than 1 and the NDP
- * count of S1 is smaller than this distance. Otherwise there would
- * have been no loss. Hence it is only necessary to see whether there
- * are further missing data packets between S1/S2 and S2/S3.
+ * At this stage we know already that there is a gap between S0 and S1
+ * (since S0 was the highest sequence number received before detecting
+ * the loss). To recycle the loss record, it is thus only necessary to
+ * check for other possible gaps between S1/S2 and between S2/S3.
*/
- int d2 = tfrc_rx_hist_delta_seqno(h, 1, 2),
- d3 = tfrc_rx_hist_delta_seqno(h, 2, 3),
- n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,
+ u64 s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
+ s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
+ s3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_seqno;
+ u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,
n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;
- if (d2 == 1 || n2 >= d2) { /* S2 is successor to S1 */
+ if (dccp_loss_free(s1, s2, n2)) {
- if (d3 == 1 || n3 >= d3) {
- /* S3 is successor of S2: entire hole is filled */
+ if (dccp_loss_free(s2, s3, n3)) {
+ /* no gap between S2 and S3: entire hole is filled */
h->loss_start = tfrc_rx_hist_index(h, 3);
h->loss_count = 0;
} else {
@@ -353,7 +336,7 @@ static void __three_after_loss(struct tfrc_rx_hist *h)
h->loss_count = 1;
}
- } else { /* gap between S1 and S2 */
+ } else { /* gap between S1 and S2 */
h->loss_start = tfrc_rx_hist_index(h, 1);
h->loss_count = 2;
}
--
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